Chapter 5

Question 1

What is one problem with facial detection on a computer?

Answer 1

Can recognize a mismatch between faces if the faces are straight on… much harder if they are angled. They are also fooled by makeup.

Question 2

What was one attempt at having better computer vision?

Answer 2

Spatial layout systems- get okay results, ofte they aren’t so good. Can find borders well but can’t find objects.

Question 3

Why can’t spatial layout systems find objects?

Answer 3

1) Image clutter-many objects are partially occluded by others. 2) Object variety- there are tons of different versions of the same thing (trees!)
3) variable views- different retinal images depending on our viewpoint, object orientation, lighting conditions etc
4) retinal stimulus is ambiguous (inverse projection)

Question 4

What is the inverse projection problem?

Answer 4

The task of determining the object that caused that particular image on the retina-impossible to solve using only bottom-up perception!

Question 5

What was Stephen Palmer’s experiment?

Answer 5

Asked participants to name line-drawn objects, but first they were shown a scene (told to ignore it). Scene was appropriate or inappropriate for the object, and there were also 2 types of objects (ones that look similar and ones that don’t)

Question 6

What were the results of Stephen Palmer’s study?

Answer 6

Performance (object identification) was faster and more accurate after seeing appropriate context (80% versus 40%) . Also, if the object was presented briefly, people mistake the incorrect, but similar object for the appropriate one.

Question 7

What happened in the follow-up study to Palmer’s experiment that asked peole to draw the object they saw?

Answer 7

It ends up looking more like the object appropriate to the scene.

Question 8

What are top-down models of perception?

Answer 8

Perception is influenced by existing knowledge, goals, expectations.

Question 9

What are the steps of top-down perception?

Answer 9

Expectation—> formulate perceptual hypothesis—->Examine features to check hypothesis—-> recognize stimulus. (ex: seal trainer versus ballroom dancer demo)

Question 10

How does context work in top-down perception?

Answer 10

The context in which something appears guides how we will perceive it (ex: ink blots over certain letters of a word, examine other letters to decide what is MOST likely.

Question 11

What are the 3 parts of top-down perception?

Answer 11

1) context
2) attention
3) organization and structure.

Question 12

What is the jumbled word effect? (context)

Answer 12

Ability to read words in sentences despite having mixd up letters in the middle of words

Question 13

What is a perceptual set? (context)

Answer 13

Readiness to perceive things in a certain way (ex: Harold Kelly’s guest lecturer, blind date).

Question 14

What are perceptual constancies?

Answer 14

Tendency to experience the same, stable perception despite changes in sensory input (ex: size constancy, colour constancy, brightness constancy)

Question 15

What is colour constancy?

Answer 15

Colour is not determined solely by wavelengths of light entering the eye-colour is perceived as constant across different lighting

Question 16

What is brightness constancy?

Answer 16

When we subtract out a shadow and see something as being the same brightness across different lighting.

Question 17

What is inattentional blindness? (attention)

Answer 17

Failure to register unattended stimuli in consciousness (ex: Gorilla video)

Question 18

What kinds of things grab our attention best?

Answer 18

Things of evolutionary importance (threatening faces, sexual things)

Question 19

What are the 2 parts of object recognition?

Answer 19

1) Perceptual organization: Representing edges and regions, figure vs ground, perceptual grouping (gestalt), perceptual interpolation
2) Object recognition (INCLUDES TOP DOWN AND BOTTOM UP)

Question 20

What is edge extraction?

Answer 20

Process by which visual system determines the location, orientation, and curvature of edges in the retinal image.

Question 21

What are the 2 areas of the visual brain that deal with edge extraction?

Answer 21

V1= orientation
V4= curvature

Question 22

Can we identify objects based only on edges?

Answer 22

no! This is only the first stage. Shadows can cause differential firing patterns not related to edges, so we need more processing to identify objects

Question 23

What is figure ground organization?

Answer 23

Must determine which objects are figures and which are ground.

Question 24

How do we usually perceive figures?

Answer 24

As being on top of a continuous background, and the edges we see are normally part of this figure-so we must assign ownership to the edges detected.

Question 25

What are the things that can determine figure ground determination?

Answer 25

Depth (the closer object is perceived as the figure), Surroundedness (completely surrounded object is seen as the figure), Symmetry (Regions with symmetrical borders are seen as the figure) Convexity (regions with mostly convex borders are typically perceived as the figure), meaningfullness (visual system recognizes object before assigning ownership)

Question 26

What is perceptual grouping?

Answer 26

Single objects being broken into many separate regions within the retinal image. Combines separate regions into a perception of the whole object.

Question 27

What are the Gestalt Laws based off of?

Answer 27

Ideas from top-down perception; the whole is greater than the sum of it’s parts, knowledge of physical laws of the world influences our perception.

Question 28

What is the law of continuity (or good continuation)

Answer 28

Points that, when linked together, would make a straight or smoothly curved continuous line are seen as “belonging together”.

Question 29

What is the law of proximity?

Answer 29

Elements that are near one another tend to be perceived as going together.

Question 30

What is the law of similarity?

Answer 30

Similar elements tend to be grouped together (colour, orientation, size etc)

Question 31

What is the law of common fate (or common motion)

Answer 31

Elements that move in unison are likely to be perceptually grouped (same speed, same direction).

Question 32

What are the laws of symmetry and parallelism?

Answer 32

Elements that are symmetrical (or parallel) tend to be grouped together. (also important in figure vs ground)

Question 33

What is the law of common region?

Answer 33

Elements within the same region tend to be grouped together

Question 34

What is the law of uniform connectedness?

Answer 34

A connected region with the same visual properties (ex: lightness, colour, texture) is perceived as a unit.

Question 35

What is perceptual interpolation?

Answer 35

Process of filling in edges and surfaces that aren’t visible- often due to occlusion or sometimes blending in with background.

Question 36

What is edge completion (perceptual interpolation).

Answer 36

The perception of a partially hidden edge as being complete-sometimes called illusory contours (relates to law of closure)

Question 37

What is surface completion (perceptual interpolation)?

Answer 37

Perception of a partially hidden surface as being complete (this one isn’t a trick of the eye, you don’t think that you can see the edges, you know that it’s a complete object)

Question 38

What is the law of meaningfulness/familiarity?

Answer 38

Combines many Gestalt Laws, tend to perceive things in terms of meaningful/familiar groupings.

Question 39

What is the Principle of Pragnaz?

Answer 39

The overarching Gestalt Law-law of simplicity. Tend to perceive things such that the resulting structure is as simple as possible.

Question 40

What does modern perception research focus on?

Answer 40

Properties of our environment, we see what is common in our environments.

Question 41

What is regularities is perception affected by?

Answer 41

Physical and Semantic

Question 42

What is the oblique effect (physical regularity)?

Answer 42

People are more accurate in estimating and perceiving horizontal and vertical lines-they are common in the physical world.

Question 43

What is the light-from-above assumption? (physical regularity)

Answer 43

We generally perceive indentations and protrusions by assuming that light is hitting them from above because light typically comes from above in our world!

Question 44

What are heuristics?

Answer 44

A best guess that usually gives us the right answer

Question 45

What are semantic regularities?

Answer 45

“meaning” of a scene or object relates to what it does, where it’s used, and what happens in that place (scene schema)